1. Field of the Invention
The present invention relates to an artificial sphincter used, for example, when the anal sphincter has been removed or when there has been a decline in the functioning of a sphincter.
2. Description of the Related Art
Conventionally, in cases such as when development of the anal sphincter is incomplete due to infantile rectal/anal malformation or when the anal sphincter is removed due to colonic cancer as an adult, an artificial anus is used.
An artificial anus commonly used conventionally is formed by sewing the intestine so as to open out at the surface of the body, and then attaching a pouch to the surface of the body so as to cover this intestinal opening.
With all pouches available on the market, the whole or part of the pouch must be replaced after defecation, and an unpleasant odor may leak out. Due to such problems, there is a drawback that everyday social life becomes troublesome.
There are artificial anuses having a stopper for which pouch replacement is not necessary. With these artificial anuses, a T-shaped cover is set into a flange that covers the aforementioned intestinal opening. There is an inconvenience in that, every time defecation occurs, the cover must be removed and then reattached. Moreover, there is also the possibility of excrement or gas leaking out from gaps between the cover and the opening.
To resolve the drawbacks of the pouch method, an artificial anus has been proposed in which an intestine opening/closing portion comprising a shape memory alloy is provided around an intestinal opening in the body, and the intestinal opening on the surface of the body is heated by passing a current from a battery embedded in the body, thus changing the shape of the shape memory alloy and opening/closing the intestinal opening (Japanese Patent Application Laid-open No. H4-319349; hereinafter referred to as ‘Prior Art Document 1’).
With the artificial anus of Prior Art Document 1, the scope of activity of the patient is widened, with no removal or replacement being necessary after defecation, and moreover because a shape memory alloy is used, a sufficient constricting force can be generated, resulting in excrement leakage and unpleasant odors being prevented.
With an artificial anus such as that disclosed in Prior Art Document 1, in which an intestine opening/closing portion comprising a shape memory alloy is provided around an intestinal opening in the body, and the intestinal opening on the surface of the body is heated by passing a current from a battery embedded in the body, thus changing the shape of the shape memory alloy and opening/closing the intestinal opening, a ring-shaped shape memory alloy element is used, and the structure is such that the intestinal opening is closed when the shape memory alloy is squashed flat. The power source for heating is covered in a case of a material having good affinity with living bodies, such as a polysulfone, and a small battery and a push switch are provided inside.
In this way, heating is carried out by passing a current from the small battery embedded in the body, thus changing the shape of the shape memory alloy and opening/closing the intestinal opening.
However, the shape memory alloy (SMA) ring used here has locally large distortion and poor repetition characteristics, making it difficult to change the shape repeatedly. Moreover, when a shape memory alloy element is embedded in a narrow region, namely an intestinal opening on the surface of the body, the intestine is subjected to a local force, and there is thus a risk of damage to this part of the body.
Moreover, the power source for heating is embedded between the skin and the muscularis, meaning that replacement when the small battery has been exhausted is troublesome. In particular, the small battery and the push switch that constitute the power source for heating are connected to the shape memory alloy (SMA) ring via a lead wire, and so the choice of installment location is somewhat limited.
Furthermore, the lead wire must be a certain length, and there is a risk of infection along this part.
One could also envisage transmitting electrical power into the body from a power source outside the body via a lead wire, but then there would be a risk of infection from the electrode part passing through to the outside of the body.
Moreover, even in the case of a 2-way shape memory alloy, it is difficult to achieve a quantity of shape change from the state in which the ring is squashed flat such that the opening opens to a sufficient size for unimpeded defecation to be possible.